Electrical switches such as pushbutton or rotary switches used for the control of industrial equipment are typically mounted on a front panel of a cabinet so that the manipulated portion of the switch (termed the "operator") projects out from and is accessible at the front of the cabinet, but the contacts of the switch and wiring to the contacts is protected within the cabinet.
For a single piece pushbutton switch, a hole may be punched in the cabinet of sufficient diameter to accommodate the pushbutton and a surrounding threaded flange. The flange and pushbutton are inserted through the cabinet from the inside and a threaded retaining nut is placed over the flange on the outside of the cabinet and tightened on the flange to securely affix the switch to the panel. The panel is thus sandwiched between the switch body and the retaining nut. For rotary switches, the operator lever may be designed to be smaller than the hole in the panel, so as to fit through the hole, or may be detachable from the operator.
A multi-piece pushbutton switch, conforming to the international "IEC standard", has an operator which may be separated from its contact blocks and installed through the front of the panel. Only the shaft of the operator extends through the panel and hence there is no size limit on the size of the actual pushbutton imposed by the hole. For example, the hole in the panel is typically only 22.5 mm and yet permits the use, for example, of an operator with an integral 40 mm mushroom pushbutton head.
Typically the detachable operator, terminating in a flange surrounding the pushbutton or lever, is inserted through a hole in the panel and secured from behind the panel with a nut so that the panel is held between the nut and the flange. The end of the operator protruding inside of the panel is snapped into one side of a latch element. Various contact blocks, depending on the particular configuration desired, are snapped onto the other side of the latch.
In order to facilitate connecting the necessary wires to the contact blocks, the latch and contact blocks may be unsnapped from the operator by pulling the latch away from the operator. Once the necessary wires are connected to the contact blocks, the latch and contact blocks may be reattached by snapping to the operator. The snap fastening is obtained by the use of detents on the latch which engage corresponding detent surfaces on the operator assembly. Such a fastening technique permits the switches to be placed closely together because no clearance around the switch is required for the assembly of the operator to the contact blocks.
Although this snap fastening approach is extremely flexible and convenient, the physical mounting of the switch elements to the panel is not as robust as the one piece switch described previously where the operator is permanently affixed to the contact blocks.